arm64: stacktrace: split unwind_consume_stack()

When unwinding stacks, we use unwind_consume_stack() to both find
whether an object (e.g. a frame record) is on an accessible stack *and*
to update the stack boundaries. This works fine today since we only care
about one type of object which does not overlap other objects.

In subsequent patches we'll want to check whether an object (e.g a frame
record) is on the stack and follow this up by accessing a larger object
containing the first (e.g. a pt_regs with an embedded frame record).

To make that pattern easier to implement, this patch reworks
unwind_find_next_stack() and unwind_consume_stack() so that the former
can be used to check if an object is on any accessible stack, and the
latter is purely used to update the stack boundaries.

As unwind_find_next_stack() is modified to also check the stack
currently being unwound, it is renamed to unwind_find_stack().

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Puranjay Mohan <puranjay12@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20241017092538.1859841-10-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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